The present invention relates to a ceramic color composition and a method of forming a ceramic color film on a glass plate using the ceramic color composition.
Hitherto, various ceramic color compositions in the form of paste have been proposed to be applied to, for example, a peripheral portion of an automobile window glass pane by the screen-printing. The ceramic color composition coated on the glass pane is dried and then baked so as to form thereon a ceramic color film. This film provides the glass pane with a colored and opaque portion and thus serves to prevent deterioration of an adhesive such as urethane sealant due to ultraviolet rays and to conceal, for example, a terminal of heating strips. A ceramic color composition in the form of paste comprises an amorphous or crystallizable glass powder, an inorganic pigment and an organic vehicle.
For example, JP-A-55-62824 discloses a ceramic color composition comprising A parts by weight of an inorganic pigment and B parts by weight of a low melting point glass powder, which are dispersed in a paste containing a resin and an oil, wherein the ratio of A/(A+B) ranges from 0.30 to 0.65.
Recently, there is an increasing demand to produce curved automobile window glass pane. Thus, hitherto, various press bending methods have been proposed to bend an automobile window glass pane. In a press bending method, the glass pane is pressed between male and female press molds provided with refractory glass cloths. However, in case that the glass pane coated with a ceramic color composition is pressed to bend the same, the ceramic color composition tends to stick to a press mold. This impairs a so-called releasability of the ceramic color composition from the mold and causes defect of a ceramic color film on the glass pane and uneven curvature of the glass pane. The ceramic color composition disclosed in JP-A-55-62824 is unsatisfactory with respect to the above-mentioned releasability, acid resistance, etc. To improve releasability, there is provided a method in which a releasing agent is applied to a surface of a ceramic color composition coated on the glass pane or to a surface of a press mold. However, this method increases the working step and the production cost.
JP-A-3-285844 discloses a ceramic color composition and a method of forming a ceramic color film on an automobile window glass pane using the ceramic color composition. The ceramic color composition comprises 5-30 wt % of a refractory inorganic pigment powder, 70-95 wt % of a crystallizable glass powder and 0-10 wt % of a refractory filler powder. The crystallizable glass powder comprises, by weight, 13-29% of SiO.sub.2, 0.1-5% of the total of Al.sub.2 O.sub.3 and La.sub.2 O.sub.3, 50-75% of PbO, 4-20% of the total of TiO.sub.2, ZrO.sub.2 and SnO.sub.2, 0-6% of B.sub.2 O.sub.3, 0-5% of the total of Li.sub.2 O, Na.sub.2 O and K.sub.2 O, 0-5% of the total of MgO, CaO, SrO and BaO, 0-5% of P.sub.2 O.sub.5 and 0-2% of F. According to the method of JP-A-3-285844, the ceramic color composition is applied to a certain portion of an automobile window glass pane. Then, the coated glass pane is heated at a temperature ranging from 500.degree. to 620.degree. C. so as to fuse the ceramic color composition. Then, the coated glass pane is heated at a temperature ranging from 600.degree. to700 .degree. C. so as to crystallize the ceramic color composition. Then, the heated glass pane is bent by a press machine. However, it is difficult to obtain a desired color of a ceramic color film. For example, a gray color is unwillingly obtained instead of a black color due to the color of lead titanate or of lead silicate. Furthermore, the temperature at which the ceramic color composition is crystallized is limited. Therefore, the temperature range for the bending is narrowed.
JP-A-3-5337 discloses a method of bending a glass plate. In this method, a ceramic color ink kneaded with an inorganic substance (quarts gel or silica gel) having a particle size ranging from 5 to 60 .mu.m and a softening point not lower than 650 .degree. C. is applied to a glass plate to form a printed layer. Then, the coated glass plate is heated at a temperature close to the softening point and a surface of a bending mold coated with a cloth of glass fiber is pressed against the coated glass plate to bend the glass plate.